Method of forming precision bore glass tubing



Jan. 11-, 1949. 5. J. EVERETT 2,458,934

- METHOD OF FORMING PRECISION BORE GLASS TUBING" Original Filed Nov. 22, 1941 ATTORNEY m m w L 1 b M Q S 9 3 L I v v v E v R m ow E .1 i V f ow GBDHH H HH I n LNRqUHHHRBfi hQWRP lHUHHU HHUI I I l hH l l HL 4 vwmnfi E E Patented Jan. 11, 1949 I METHOD orroaMlNe-ranolsron BORE IGL'ASSJIEUBING q Samuel James Everett, Thornton Heath, England,

assignor to James A. Jobling-'& Co. Ltd., Sunderland, England,-a British company Original application November 22, 1941, Serial. No. 420,121. Divided and this application December 28, 1945, Serial No. 637,572. In Great Britain February 8, 1941 9 1 This invention relates to plastic tubes, particularly glass, tubes and comprises matter divided from application for Letters Patent Serial No. 420,121, filed November 22, 1941, now Patent No. 2,393,979, issued Februmy 5, 1946. That application is concerned with apparatus for manufacturing glass tubes that have extremely accurately shaped internal surfaces, that is to say have'surfaces that are absolutely true and smooth, with the fine quality that can be obtained by grinding and lapping or polishing. Plastic material that is particularly suitable for this purpose is ordinary glass or low-expansion glass and the tubing made both in accordance with the aforesaid patent application and with the present application can conveniently be employed for the cylinders of hypodermic syringes.

According to the present invention, a method for providing a, pre-formed thermoplastic tube with a fine quality internal surface comprises the steps of moving the tube over and-in engagement with a surface having the dimensions of the desired internal dimensions of the tube, heating the tube in the vicinity of its engagement'with said surface, and controlling the speed of move-5 ment of the tube so that the movement in the di rection away from said surface is greater than that toward said surface. The initial tube or cane preferably has a, greater internal diameter than the said surface and the wall thickness-of the tube is generally somewhat greater than the wall thickness of the finished tube. Then, asthe heated tube is drawn over said surface or former,

and absolutely smooth surface, may conveniently be arranged so that it projects horizontally into the furnace for heating the glass. When a ,tube of circular cross-section is being made, it is preferred to cause the former to rotate about its axis, but when a tube of non-circular cross-section is being shaped the former, of course, cannot be rotated.

In order that the invention may be clearly understood and readily carried into efiect, arrangements in accordance therewith will now be described, by way of example, with reference.

to the accompanying drawings, in which- Figure 1 is a side elevation of a part of the apparatus for use when carrying the invention into effect, I

Figure 1A is a side elevation of the remaining The former,

6 Claims., (01. 49-84) the manufacture 'of v I part of the apparatus shown in Figure 1 for use when. carrying the invention into effect, and

-Figure 2 is a cross-section on an enlarged scale of a detail of the apparatus in Figure 1.

The apparatus shown in Figures 1 and 1A is arranged for the purpose of shaping the internal surfaces of glass tubes, and, is constructed so that the glass tube I being treated is supported between chucks 2 and 3, which are fed along guides 4 and 5 to carry the glass tube I through a furnace 6 where the tube is heated sufficiently to cause it to become plastic. The effect of this is to cause the internal surface of the tube to conform accurately to the external surface of a former! over which the tube passes as it travels through the furnace 6. The former l is carried by a rod 8 that projects through the chuck 2 and into the glasstube I.

, Each of the chucks 2 and 3 contains a pack of rubber rings 9, as shown in Figure 2 in which the details of the chuck 2 appear. The pack of rubber rings 9 is contained between an annular abutment I lla on a sleeve i it and a gland member H,,which is tightened upon the rings 9 in an axial direction so that they expand internally and grip the tube. The axial tightening of the gland member H is efiected through the medium of finger nuts lz'thatbear on the member l i and are threaded upon studs i3 secured to the sleeve Ill. -The gland member I l is formed with a central passage liwhichreceives a-T-piece E5, the limb l6 of which is connected by a flexible pipe lta to a vacuum pump l8 driven through a driving belt IT by an electric motor 59. The rod '8 that supports theformer 'l passes through the horizontal portion of the T-piece E5 to worm reduction gearing 2B, whereby'the motor i9, acting througha driving belt'2 l, is enabled to rotate the rod 8 and former '1' about their common axis.

To enable the vacuum pump l8 to maintain ai'reducedv pressure'in the pipe l, a seal is provided between the T-pi-ece l5 andthe rod 8.-

the seal consistinggas shown in Figure 2, of an appropriate flexible'sleeve 22 bound upon one end of the T-piece "l5 and upon the rod 53, The friction between the sleeve'22 and the rod 8, how ever, is not so great that the latter cannot turn relatively-to the sleeve;

Thevacuum pump l3, by exhausting the air from inside the tube I, prevents corrosion of the former 'I,"any oxygen within the tube i being substantially exhausted by the pump 5 B, and en ables the outside air pressure to assist in the closing'ofthe tube l o'nto the former l, it being understood that the internal diameter of the tube I is initially slightly greater than the external diameter of the former.

It will be seen that the former 1 projects a few inches out of. the, furnace .,&,.on the.,di scharge side thereof sq as to give supjportf, to,- the tube until it has Substantially solidified. Suitable materials for the former "I are pure silica, the. metal alloy known under the registered trademark Inconell, and stainlesss'tela'i Whenithe former is made of pure silica, it is slightly tapered in the direction of the movement of the tube, When it is made of an alloy. sush ias stainlfifis; steel, it is convenient to use an untaperedzformerc. because, when the apparatus is in oneration the part of the former that projects. frointne nace 6 is cooler than the parhofi'the ftirr'ne ing; within the furnace 6. The former, therefore,

expands unevenly along its length and becomes. slightly tapered as is required to enable the tube to be more easily drawn off the former. Furthermore, it is advantageous to coatthe bore ofthe: tube with colloidal graphiteso' a's to' en'ablethe tube-to slide more readily on the former. In the example beingdescribedi the former rotates at. 79- revolutionsperminute and therotation of the formerqensures that. the inner surface of" the tube shall be. round; even if the'forrner isuriot.truly so (measurements of" the order of 0300001 inch being -considered in-thiscorinectionl It.has-been found: advantageous to provide therdtating-former-with a narrow flat surface along one's'ide so that the cross-sectionof the formerappears as a circle-with'a small segment removed.

The-chuck 2 is supported by a carriage- 23, thespeed ofthe carriage-23 alongtheguide (being controlled by a lead screw 2'4; whil'e theegl'asstube l-i's' drawn through the. furnace B -by the chuck 3, which is supported by forwardly extendingarms '25: from a carriage 2B dri'ven along the guideii'by. a lead screw- 21. li he lead screws and 2'l-are driven-from a couritershaft '2 8; drivenby a motor 29'. The-connection between the in'otor: and countershaft includes a belt 30; a 19:1 wormreduction: gear- 3.1; and stepped conepul-. leysx 32 and :331 permitting some-variation in: the speed ratio between the motor 29 and the coun tershaft 28', sothat the'resultant speed at which the glass tube l passes through the furnace maybe adjusted. The arrangement is suchthat the pulley 32; rotatesat .20 revolutions per minute..and. the speed of the countershaft canbe varied between andi'2'0 revolutions per minute. The countershaft'. 28-; drives the lead. screw 21 at an equal speed through the medium of pulleys-- 341 and.-35'; connected byta'belt'36; The gear ratio between thecountershaftlk: and theothev lead screw 24; however, i'svariable through: the medium of stepped conepulleys 3?! and '38 connected by a belt 39. Therefore, the-relative-movemerit between the chucks 2. and 3:cani'be: altered to adjust the amount-the glass tube is stretched, as it'passes through the furnace 6.

The threaded .members .on' the carriages 23 and 25-are constructedsoithatizthey can-be put: into or out of engagement with. the'lead screwsflr-an'di'fl. Accordingly; the-chuck -2 can readily be moved to the-1eft,:as; viewed: in Figure I, and the glass cane (standard glasscane's are-five feet. long). to :be treated may berpassedmhroughz' the furnace- 6;and overthezformen'l towbe secured: at,

itstleft handendxin .thes chuck; 2-, .the chuck 3: thenv being movedzclose to the furnace't-fi. so 'asto receive the right :ha-ndend. offithe tube err-cane- I. The motorl9 is-started soxthat thexformer: l is: rotated and-the air exhausted froim thexrear e'nth eo ntrolled to heat the glass to about 800 C. The gearing-betweenthe motor 29 and the chucks 2 and '3- -is such that the chuck 2 can be arranged tomove ataspeed. of; from 2% to 10 inches per miinflic while,the, chuck 3 can be arranged to move'at aaspeed of from 5 to 10 inches per minute. Generally the speed ratio is so contrived "that the chuck'S'moVes substantially faster than the chuck .2. In. action, both chucks move from lef tttolrightuaswiewed in Figure 1, and, therefore the guide 5 is made longer than the guide 4. In anexamp'le where the initial tube or cane weighs 16 ounces and has an internal diameter of about 51 withla wall thickness of about 2 um/m: the finishedi-tube-has anaccurate bore: of diameter-.and a wall; thickness of 1 m./m. In the treatment. of: this. tube, therefore, itslength is approximately doubled.

To adlustitheinternal diametenof the tube, the former If may be taperedby approximately one two-thousandth. of. an-inch: in its length of approximately eight. toxten. inches. Then the reqyi iedgadjustmentmay be effected. by moving the former: longitudinally." with respect to the furn ace-n. This may; be accomplished by screwing the rod,8 intoithe. worm 20.111 order to vary theposition; of; theiformer slightlywith respect to the area in. which the: glass isin a semi-plastic condition. If the. formerisvery slightly tapered, a very slight. adjustmentin the diameter of the internal surface is obtained.

I. claim: Amethod; fonproviding a pre-formed thermoplastic? tube with a fine quality internal surface. comprising the steps of moving the tube over andv in engagement with a surface having the dimensions ofthe desired internal dimensions ofisaid' tube, heating the tube in the vicinityof itsengagement with said surface, and. controlling the-speed of movement of the tube so that the-movement inthe direction away fromsaid surface ls'greater thanthat toward saidsurface.

2. A method for-providing a pre-formed thermoplastic tube with a fine quality internal surface comprisingthe steps of moving thetube m-a longitudinal direction, positively limiting the controlling the rate of movement of the tube so that the movement from the area. of

p'qsitivelimitation is greater than the rate of,

movement toward it.

3; A method of providing a pro-formed thermoplastic tube with a fine quality internal surface-comprising the stepsof moving the tube in-a longitudinal direction over and'in engagement wit-ha surface, rotating said surface about the axis of said tube. so that said surface traces a figureof circular cross-section the outer dimension oiwhichjs. equaltothe desiredinner.

dimension of. the finished tube, heating the tube in the vicinity, of said engagement with said surface, and controlling the rate of longitudinal movement of: the: tube. so that said' movementfrom the area of heating is greater than the rated-movement. toward said area of heating;

4. A method of providing a pre-formed thermoplastic tube with a fine quality internal surface comprising the steps of moving the tube in. a longitudinal direction over a surface of less diameter than the internal diameter of the tube, rotating said surface about the axis of said tube, heating the tube in the vicinity of said surface, and controlling the rate of longitudinal movement of the tube so that said movement from the area of heating is greater than the rate of movement toward said area of heatingflthereby reducing the diameter of said tube and causing engagement of same with said rotating surface.

5. A method for providing a pre-formed thermoplastic tube with a fine quality internal surface comprising the steps of moving the tube in a longitudinal direction over and in engagement with a surface, rotating said surface about the axis of said tube so that said surface traces a figure of circular cross-section, the outer dimension of which is equal to the desired inner dimension of the finished tube, heating the tube in the vicinity of said engagement with said surface, controlling the rate of longitudinal movement of the tube so that said movement from the area of heating is greater than the rate of movement toward said area of heating, and evacuating said tube beyond said surface.

6. A method for providing a pre-formed thermoplastic tube with a fine quality internal surface cdinprising the steps of movin at a given ratefof speed, the rearward end of said tube toward and over a tube engaging surface of smaller crdss-section than said tube, heating the tube in the."; vicinity of its engagement with said surface, withdrawing the forward end of said tube froni said engaging surface at a speed greater than itsHfirst-mentioned speed-thereby causing said tube to contract onto said surface, and evacuating said tube beyond said surface.

SAMUEL JAMES EVERETT.

, L ner-cannons CITED The wing references are of record in the file o "tIiisf patent:

a STATES PATENTS Number a: i: 

